Hello
Ground loop typically generates hum - 50Hz in Europe - 60Hz in USA and some other places . . .
But because the mechanism of ground loop is that two points are connected via two or more routes, there is a loop - and the omnipresent electric field emanating from electric motors, transformes, light fixtures, house wiring etc. goes through that loop and generates electricity, that becomes audible, if circuitry is high impedance enough.
The ground loop within your guitar is small - so nothing to worry about - it would only produce minuscule hum - if any.
Large ground loops are typically coming up when you i.e. have pa-system with snake to f.o.h to mixer - and you provide electricity from more than one single grounded source. Like you bring your mixer across the room and notice, that there is wall outlet. Plug in and HUM! Reason being, that who knows which way the cable goes inside building, before it reaches the outlet - it can well be, that it comes from altogether different source than the outlets at stage. So the loop length might be hundreds of meters - thus providing plenty of area for that electric field to penetrate.Only way to be sure is to pull power cable next to snake to F.O.H. and use that.
But - back to your guitar - you could invest few Euros and buy a multimeter - it is very useful for checking cables, speakers etc - a 10€ unit will do. With that you can measure pickup dc-resistance, too.
Meanwhile - plug your guitar into amp, turn the amp on and volume up to comfortable level. Do not touch any metal parts - can you hear light hum/buzz from amp? Does it go away when you touch various parts of the guitar? Including strings? If yes, then you have the strings grounded.